According to the preamble of claim 1, the invention relates to a valve timing gear for an internal-combustion engine, in which a timing cam of a camshaft acts by way of a tilting segment in a tappet in a timing manner upon a lifting valve, the tilting segment constructed with a contact path acted upon by the timing cam being arranged in a movably guided manner such by way of a circular-arc-shaped section concentric to the axis of rotation of the camshaft in the tappet that, by means of a control device during each valve lift an engagement of the contact path with the flanks of the rotating timing cam, which engagement determines the opening and closing phase of the lifting valve, is achieved by a swivelling movement of the tilting segment which is forcibly controlled in the same direction and/or in the opposite direction relative to the rotating direction of the timing cam.
The above-described valve timing gear is the object of European Patent Document EP 0 626 035 B1, in which, by means of the valve timing gear described in that document, in the case of an internal-combustion engine, at lower rotational speeds, small valve opening angles with a low or small overlap and, at high rotational speeds, large valve opening angles with much overlap of the inlet and outlet valve lift curves are achieved for forming high gas dynamics. Inlet and outlet valve lift curves corresponding to a timing cam, by means of the invention, can be changed correspondingly in the case of an intermediate element or tilting segment controlled in the same direction synchronously to the respective timing cam in the direction of large valve opening angles and, in the case of an intermediately element or titling segment synchronously controlled in the opposite direction, can be changed correspondingly in the direction of small valve openings angles.
As further illustrated in the drawings of that document, each of the illustrated and described valve timing gears is combined with a control device which in each case comprises a control shaft arranged in the transverse direction of the internal-combustion engine laterally of the respective camshaft. In connection with the transmission members transmitting the control movements of the control shaft to the respective intermediate elements, an additional space requirement occurs in the cylinder head of the internal-combustion engine which, for example, does not exist in the case of a defined valve angle or results in a wider cylinder head.
It is an object of the invention to improve the valve timing gear of this type such that it can be arranged independently of the given space conditions in a specifically given cylinder head under a cylinder head cover which is maintained unchanged.
This object is achieved by means of Claim 1, specifically in that the control device comprises a slider rocker which is guided in the valve lifting direction by way of a first sliding hinge joint arranged on the engine section side and another sliding hinge joint provided on the tilting segment side and which has a control opening which is penetrated with play by a timing-cam-free section of the camshaft, an element, which can be operated in a controlled manner, of an adjusting device arranged in/on the camshaft while rotating with it being applied such to the circumference of the control opening that the slider rocker, which can be adjusted in the valve lifting direction with the control opening eccentrically to the axis of rotation of the camshaft, while the camshaft is rotating, carries out for each valve lift a periodic rocking movement which is used for forcibly controlling the tilting segment and takes place transversely to the valve lifting direction with a superimposition with a sliding movement caused in the valve lifting direction.
For a valve timing gear having lifting valves operated by way of tappets, by means of the invention, a small-sized control device is advantageously achieved for changing the valve opening angles in a manner which reduces the required space, in that the control shaft or another equally acting adjusting device with the pertaining adjusting means are arranged in and around the camshaft in a close vicinity for the periodic rocking drive of a slider rocker which acts upon the respective tilting segment in a driving manner and which is preferably guided on the other side of the camshaft by way of a sliding hinge joint on an oil supply pipe fixed on adjacent camshaft bearing covers.
In another embodiment, this slider rocker arranged in a rockingly and slidably guided manner within a given cylinder head contour, preferably within the projection of a camshaft driving wheel, has a control opening which is closed on its circumference and is designed radially symmetrically with a cylindrical circumference, for achieving advantageously symmetrical valve lift courses. As a result of the corresponding design of the control opening, as required, asymmetrical valve lift courses are also conceivable.
A constructionally and kinematically advantageous embodiment of the invention is described in additional subclaims.
The advantageously small-sized control device according to the invention kinematically has the advantage of a continuous change of the opening angle, in which case, even in the case of small opening angles, large valve lifts are achieved with a relatively low migration of the contact line between the cam and the contact path of the tilting segment. Furthermore, advantageously the same cylinder head can be used for a valve timing gear with the control device according to the invention and for a valve timing gear without this control device, in which case, particularly when a valve timing gear is used which has two adjacent lifting valves of the same time while no control device is provided, no unnecessary and empty constructional volume is carried along. Finally, a valve timing gear with the control device according to the invention can also be equipped with an angle-of-rotation adjusting device for spreading the timing cams.
Because of the low oscillating mass, the special advantage of the control device according to the invention is its suitability for high-revving internal-combustion engines.
The invention will be described by means of a preferred embodiment illustrated in the drawings.